Modified Submarine Strengthens Sweden's Impact in the Baltic Sea
(Source: Swedish Armed Forces; issued May 15, 2020)
(Unofficial translation by
Sharper, quieter and more efficient. The modified submarine HMS Gotland has now been delivered to the Swedish Armed Forces. (Saab photo)
HMS Gotland is now the most modern, quietest and most efficient submarine in the Baltic and the North Seas. Yesterday, the Swedish Armed Forces and the First Submarine Flotilla received the upgraded submarine from Saab Kockum's and the Swedish Defense Force's matériel plant.

HMS Gotland is the first of two Gotland-class submarines that have undergone a mid-life upgrade. The second, HMS Uppland, will soon be ready for delivery. The modifications include a new ship surveillance system, a new combat and fire management system, diving locks and more modern Stirling engines. This means that the submarines are even quieter, making their detection and attack more difficult.

The submarines have also been extended by two meters by cutting the pressure hull in the middle and welding it together again. The new two-meter section allows, among other things, new systems for energy optimization.

Modification of the two Gotland submarines represents a major step towards the next generation of submarines in the Swedish Armed Forces, which goes under the designation A26. The two new submarines will be renamed HMS Blekinge and HMS Skåne. Since the first submarine in the series gives its name to the entire class, the A26 becomes the Blekinge-class.

The Blekinge is currently being built by Saab Kockums. Many of the systems are the same as in the newly modified, which gives many advantages. One is, for example, the crews' ability to switch places between both types of submarine. This increases operational endurance and reduces the sensitivity of staff vacancies.


Upgraded Submarine Returns to the Armed Forces
(Source: Swedish Defence Matériel Agency, FMV; issued May 15, 2020)
(Unofficial translation by
The submarine HMS Gotland has now been re-delivered to the Swedish Armed Forces after an extensive upgrade.

The Gotland Submarines, built during the years 1990-1997, had previously undergone simpler modifications. The mid-life upgrade carried out on the two Gotland submarines takes a holistic approach and looks over the entire submarine and its installations to ensure they attain the required availability and performance for the remainder of their service life.

Systems and equipment that are outdated and deemed difficult to maintain for the remaining life have been upgraded or replaced. In connection with this, the need to update the submarine's existing capabilities to meet new threats has also been evaluated. Furthermore, the mid-life upgrade is also about meeting work environment and safety requirements that have changed since the submarines were built.

Hans Egonsson, project manager at FMV, notes that it is a comprehensive modification work carried out on the 25-year-old submarines at Saab Kockum's shipyard in Karlskrona.

“More than 10,000 drawings have been produced within the project and almost 500,000 production man-hours have been carried out, and more than 10,000 new welds have been made. In principle, the entire management system has been replaced, including all sensor and weapon systems. The program has carried out more than 1,500 hours of training and about 360 verif”ication activities of the technical systems with over 1,000 hours of system tests at sea.

Extended by two meters

The submarines are cut in half and extended by about two meters by inserting a plug in the hull. The in-house modification work has been greatly facilitated by being able to work with free access in and through the submarine sharing.

Many onboard systems have been replaced by newer generations, including not only the sensor systems but also ship systems that produce compressed air, cooling and hydraulics and that supply power to many other systems on board. The transition to digital monitoring systems and the interdependence of the systems makes the integration of the systems extremely important.

Several systems installed on the Gotland submarines are the same as those that will be installed on the two new A26 submarines that FMV will deliver to the Swedish Armed Forces. The Stirling engines are an example, but there are also passive and active sonars, connection systems and management support systems, and the optical fiber periscope that replace the old periscope.

From periscope to camcorder

The optronic mast is a video camera with a powerful magnification, where operators can see the surface image directly on the screens and also later review still and video images at leisure on a separate console, after the optics mast has been retracted.

When the crew wants to scout the surface, both for safety and for the tactical use of the boat, they send up the mast for a short time, and collect the imagery. Then the material can be analyzed afterwards.

The air-independent Stirling engine has been used in Swedish submarines for 30 years. The basic principle is still the same, but much has happened since in this area: digital control system, new generator and recovery of the residual heat in the exhaust gases to produce hot water for comfort on board are some of the measures taken.

In conjunction with the modifications, a general review and overhaul have also been carried out.


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